Estimation of the neuraminidase content of influenza viruses and split-product vaccines by immunochromatography

The neuraminidase (NA) of the influenza virus, as well as the hemagglutinin, is the most important protective components in the vaccine. However, the NA content of the vaccine remains to be standardized because of the labile nature of this glycoprotein during various chemical treatments and storage. In the present study, the NA content of the split-product (SP) vaccine (virus treated with ether then formalin) was estimated together with that of the virus by an immunochoromatography technique using monoclonal antibodies (mAbs) to viral NA for A/Panama/2007/99 (A/Pa) (H3N2), B/Shangdong/7/97 (B/S) or A/New Caledonia/20/99 (A/NC) (H1N1) viral strains. In the new method, the NA catalytic activity of each fraction from steps of NA purification was measured as an index of NA content. The NA level of A/Pa, B/S or A/NC viral particles was estimated at 6.9 ± 0.9, 7.6 ± 0.8 or 8.5 ± 1.7% of total viral protein (not significant difference between viral strains). The NA level of the corresponding A/Pa, B/S or A/NC vaccines was estimated at 9.6 ± 1.5, 12.7 ± 0.4 or 12.2 ± 1.2% of the total vaccine protein (a significant difference between each strain of virus and its vaccine). These results suggest that the NA content in the N1, N2 or B type NA virus ranges from 5 to11% of the total viral protein, and that the NA level in each split-product vaccine is 1.4- to 1.6-fold higher than that in the corresponding viral particles. They also suggest that the NA content can be estimated by the immunochoromatography technique using anti-viral NA mAbs.